Formation of the vertebrate embryo involves an intricate series of cell movements, cell proliferation, and differentiation. Morphogenesis of the vertebrate head is particularly complex-it entails participation of multiple cell types, signaling molecules, and cell-cell interactions. One of the most prominent cell types in the craniofacial skeleton of vertebrates arises from a migratory stem cell population called the neural crest. Shortly after neural crest cells are formed in the neural tube, they migrate extensively and form diverse derivatives throughout the embryo, including melanocytes, most of the peripheral nervous system (neurons and glia), as well as most of the skull and face, including cartilage, bone, and smooth muscle. Despite the developmental importance of the neural crest and the striking number of craniofacial defects that arise from aberrant neural crest development, very little is known of the mechanisms that govern the migration and differentiation of neural crest. The long-term goal of this proposal is to understand the cellular and molecular mechanisms that underlie neural crest cell differentiation during craniofacial development. Along the neural axis, there are vast differences in cell fate between cranial and trunk neural crest populations;although both can contribute to elements of the peripheral nervous system, only cranial but not trunk neural crest cells are able to contribute to osteogenic and chondrogenic lineages. We have recently isolated a cytokine, cytokine-like C17 (C17), which is prominently expressed in cartilage precursors derived from cranial neural crest but not in trunk neural crest. Studying the functions of C17 should yield important insights into craniofacial development. In addition, we have challenged the developmental potential of freshly dissociated trunk neural crest cells by grafting them into the head. Our preliminary results showed that many donor cells could differentiate into collagen II+ chondrocytes. This suggests that trunk neural crest has the capacity to differentiation into cartilage under certain conditions. The proposed experiments will investigate the differentiation of neural crest cells into craniofacial structures as well as address the fundamental question of how rostrocaudal differences in neural crest populations govern their cell fates. Our working hypothesis is that there may be molecules that differentially regulate the development of cranial vs. trunk neural crest. Specific molecular combinations could engage any neural crest to specific fates such that trunk neural crest cells might be competent to become cartilage when placed in the appropriate environment. We will test this hypothesis by: 1) characterizing the function of cytokine-like C17, a gene that is highly enriched in the head, and 2) testing the chondrogenic potential of trunk neural crest cells under different conditions. Formation of the head and face is a complex process that involves multiple tissues and genetic factors. One of the most important cell types involved is a stem cell-like population called the neural crest. Understanding how neural crest cells develop is important because common birth defects such as cleft lip and palate are caused by abnormal development in this cell type.